Method and apparatus for Spray Drying and Powder Produced Using Said Method

ABSTRACT

Method for spray drying a high-viscosity fluid product using a spraying device, wherein the method comprises projecting the fluid product out of an outflow opening of the spraying device for obtaining droplets of the fluid product, wherein the spraying device is arranged to cause a pressure drop in the fluid product across the outflow opening which is larger than 15 bar and at least partially drying the droplets in a drying medium, such as air, to become particles.

The invention relates to a method for spray drying a fluid product usinga spraying device, wherein the method comprises projecting the fluidproduct out of an outflow opening of the spraying device for obtainingdroplets of the fluid product and at least partially drying the dropletsin a drying medium, such as air, to become particles.

Methods for spray drying a fluid product are known per se. In one typeof spray drying method, the fluid product is fed to a nozzle, whichproduces a mist of droplets of the fluid product in a vessel. Thedroplets are subsequently dried, e.g. in a stream of air.

Another method for spray drying a fluid product is known from WO2005/058473. This known method comprises projecting, by means ofnozzles, jets of liquid and disturbing the jets to cause break upthereof into streams of droplets. Further, the droplets are contactedwith streams of gas to cause or allow the droplets to, at leastpartially, solidify.

The known (conventional) spray drying methods, however, have thedisadvantage that a relatively large amount of energy is required fordrying the droplets to become particles.

It is an object of the present invention to at least partially obviatethe above problem.

According to a first aspect of the invention, the amount of energyrequired for drying the droplets to become particles can be reduced byspray drying high-viscosity fluid products.

A fluid product to be spray dried usually comprises a solvent, e.g. aliquid such as water, and dry matter dissolved and/or suspended in thesolvent. In the fluid product to be spray dried, the viscosity is interalia related to the concentration of the dry matter in the solvent. Whenthe viscosity of the fluid product is high (i.e. higher than viscositiesconventionally used for fluid products to be spray dried), theconcentration of dry matter is larger than the concentration of drymatter in fluid products which are spray dried using known spray dryingmethods. Hence, according to the first aspect of the invention, thedroplets of the high-viscosity fluid product comprise less solvent thandroplets of fluid products in conventional spray drying methods, so thatless energy is required to remove the solvent from the droplets to drythe droplets to become dry particles.

Conventional spray drying methods, and spray drying equipment, are notsuitable for spray drying high-viscosity fluid products. Thehigh-viscosity fluid product prevents natural formation of droplets.Further, in methods using projecting jets of liquid and disturbing thejets to cause break up thereof into streams of droplets, use of ahigh-viscosity fluid product prevents the formation of jets and/or thecontrolled break-up of the jets into droplets.

Further, generally, the skilled person will not consider high-viscosityfluid products as starting material for spray-drying. In this light,reference is made to the review of Prof. Walzel in Chem.-Ing.-Tech. 62(1990) Nr. 12, pages 983-994, who observes that the commonly used“Hohlkegeldüsen sind für höhere Flüssigkeitsviskositäten ungeeignet”.For a 1 mm nozzle, a viscosity of 50 mPa·s is said to be the maximumviscosity.

In order to overcome this problem, according to a second aspect of theinvention the spraying device is arranged to cause a pressure drop inthe fluid product across the outflow opening which is larger than 15bar. Preferably, the pressure drop is larger than 50 bar, morepreferably larger than 100 bar, most preferably larger than 300 bar.

Hence it is possible to spray dry a high-viscosity fluid product using aspraying device, wherein the method comprises projecting the fluidproduct out of an outflow opening of the spraying device for obtainingdroplets of the fluid product and at least partially drying the dropletsin a drying medium, such as air, to become particles.

Here a fluid product to be spray dried is considered a high-viscosityfluid product if the viscosity, determined at a spray drying temperaturewhich in use prevails in the outflow opening, e.g. −50 to 300° C.,preferably 40-100° C., and a shear rate as in use present in the outflowopening, e.g. 1·10⁴-1·10⁶ s⁻¹, using a capillary viscosity meter, ishigher than 10 mPa·s, preferably higher than 25 mPa·s, more preferablyhigher than 50 mPa·s, even more preferably higher than 100 mPa·s andmost preferably higher than 200 mPa·s. Since products to be spray driedare usually shear-thinning and since the viscosity normally decreaseswith increasing temperature, it has been shown that these viscositiesmay well correspond with viscosities above 1 Pa·s at 20° C. and zeroshear.

Alternatively, or additionally, as the droplets comprise less solvent,it is also possible to dry the droplets in a shorter time. It is alsopossible to dry the droplets, after having been ejected by the outflowopening along a shorter flight path. Hence it is possible to dry thedroplets in a smaller installation, e.g. in a smaller vessel.

According to a third aspect of the invention, the step of projecting thefluid product out of the outflow opening comprises generating a fluidjet projecting from the outflow opening, and disturbing the fluid jetfor breaking the fluid jet into droplets with a narrow sizedistribution. Preferably, the step of disturbing the fluid jet comprisesvarying the pressure of the fluid product upstream of the outflowopening, e.g. by moving an end of a control element in a directionfrom/to the outflow opening, for instance at a predetermined distance of2-1500 μm, preferably 15-500 μm, to the outflow opening, for varying thepressure of the fluid product by vibrating the control element. Thus,controlled break-up of the jet into droplets is possible. The largerconcentration of dry matter in the droplets and the narrow sizedistribution further allow reduction of the amount of energy requiredfor drying the droplets, because it is not necessary to over-dry thedroplets to be sure that even the largest particles are fully dried.

Preferably, the pressure of the fluid product upstream of the outflowopening is varied at a predetermined, substantially constant, frequency.This aids in providing the narrow particle distribution. A dropletdiameter may be determined by controlling the predetermined frequency.

Hence, it is possible to generate particles with a relatively narrowparticle size distribution, e.g. a particle size distribution with amonodispersity index of less than 1, preferably less than 0.7, morepreferably less than 0.1. The monodispersity index of the particle sizedistribution is defined as (d₉₀−d₁₀)/d₅₀, wherein d₁₀, d₅₀ and d₉₀represent the 10%, 50% and 90% particle size percentiles, respectively.

A narrow particle size distribution has, inter alia, the advantage thatsubstantially all particles posses a desired property, such as goodsolubility. Further, it can be prevented that dust, i.e. particles thatare so small that they are blown into the environment, e.g. by dryingair, is produced. Hence, the yield of the spray drying process can belarger.

Preferably, the predetermined frequency is chosen such that a distancebetween two droplets consecutively ejected at the outflow opening isgreater than or equal to two times the droplet diameter, preferablygreater than or equal to three times the droplet diameter. Hence, it iseffectively prevented that droplets coagulate after being formed. Thus,the narrow size distribution is better maintained.

Preferably, the predetermined frequency is chosen such that a distancebetween two droplets consecutively ejected at the outflow opening issmaller than or equal to eight times the droplet diameter, preferablysmaller than or equal to four times the droplet diameter. Hence,droplets can be produced at a high repetition rate.

According to a fourth aspect of the invention, the step of projectingthe fluid product out of the outflow opening comprises providing thefluid product to an outflow opening at a predetermined feed pressure.Preferably, the feed pressure is kept substantially constant. Thisprovides the advantage, that a jet is formed wherein break-up intodroplets is not influenced by variations in the feed pressure. Thus, thenarrow size distribution is better maintained.

The feed pressure may be kept substantially constant by means ofapplying pressure to the fluid product hydraulically or pneumatically.Hydraulically is understood to mean: using a liquid; and pneumaticallyis understood to mean: using a gas. Through the ability to apply thefeed pressure to the fluid product utilizing a gas and/or a liquid, thefluid product can be supplied to the outflow opening in a stable mannerat a very high pressure of e.g. more than 15 bars.

Alternatively, or additionally, the feed pressure may be keptsubstantially constant by means of a pump.

According to a fifth aspect of the invention, the method may compriseprojecting the fluid product out of a plurality of outflow openings ofthe spraying device for obtaining droplets of the fluid product. Hence,it is possible to increase the volume of fluid product per unit timethat can be spray dried using the method.

According to a sixth aspect of the invention, the viscosity of the fluidproduct, determined at the spray drying temperature which in useprevails in the outflow opening, e.g. −50 to 300° C., preferably 40-100°C., and a shear rate as in use present in the outflow opening, e.g.1·10⁴-1·10⁶ s⁻¹, using a capillary viscosity meter, is higher than 10mPa·s, preferably higher than 25 mPa·s, more preferably higher than 50mPa·s, even more preferably higher than 100 mPa·s and most preferablyhigher than 200 mPa·s. Hence, a high-viscosity fluid product can bespray-dried.

Further, preferably a transverse dimension, e.g. a smallest transversedimension such as a diameter, of the outflow opening is smaller than orequal to 150 μm, preferably smaller than or equal to 100 μm, morepreferably smaller than or equal to 80 μm. Hence, it is possible toproduce relatively small droplets, e.g. droplets with an average sizesmaller than or equal to 250 μm.

In a special embodiment, the viscosity of the fluid product, determinedat the spray drying temperature which in use prevails in the outflowopening, e.g. 40-100° C., and a shear rate as in use present in theoutflow opening, e.g. 1·10⁴-1·10⁶ s⁻¹, using a capillary viscositymeter, is higher than 30 mPa·s, while the transverse dimension, e.g. thediameter, of the outflow opening is smaller than or equal to 100 μm.

The invention further relates to a powder produced using the methodaccording to the invention and an apparatus for spray drying ahigh-viscosity fluid product

Further details, aspects and embodiments of the invention will bedescribed, by way of example only, with reference to the drawings.

FIG. 1 shows an example of a first embodiment of an apparatus for spraydrying a fluid product according to the invention.

FIG. 2 shows an example of a second embodiment of an apparatus for spraydrying a fluid product according to the invention.

FIG. 3 shows an example of a third embodiment of an apparatus for spraydrying a fluid product according to the invention.

FIGS. 4 a-4 g show examples of plan views of a plurality of outflowopenings of embodiments of a spraying device according to the invention.

FIG. 1 shows an example of a first embodiment of an apparatus 1 forspray drying a fluid product according to the invention. The apparatus 1comprises a spraying device 2. In this example, the spraying device 2 isin fluid communication with a product supply line 4, for supplying thefluid product to be spray dried to the spraying device 2. The sprayingdevice 2 is arranged for projecting the fluid product out of an outflowopening 6 of the spraying device for obtaining droplets 8 of the fluidproduct. In this example, the spraying device 2 projects the droplets 8into a vessel 10. Here, the vessel 10 forms drying means for allowingthe droplets 8 to dry to become particles. It is also possible that theapparatus comprises drying means for causing the droplets 8 to dry tobecome particles, e.g. supply means for drying air. Such supply meansmay e.g. provide drying air flowing along with the droplets or in acounter flow flowing opposite to the direction of the droplets.

In use, the fluid product to be spray dried is supplied to the sprayingdevice 2. According to the invention the fluid product is ahigh-viscosity fluid product. The viscosity of the fluid product ishigher than 10 mPa·s, preferably higher than 25 mPa·s, more preferablyhigher than 50 mPa·s even more preferably higher than 100 mPa·s, mostpreferably higher than 200 mPa·s, determined at the spray dryingtemperature which in use prevails in the outflow opening, e.g. −50 to300, in this example 40-100° C., and a shear rate as in use present inthe outflow opening, e.g. 1·10⁴-1·10⁶ s⁻¹, in this example 5·10⁵ s⁻¹,using a capillary viscosity meter.

In this Example a smallest transverse dimension, such as a diameter, ofthe outflow opening 6 is smaller than or equal to 150 μm, preferablysmaller than or equal to 100 μm, more preferably smaller than or equalto 80 μm.

Hence, it is possible to spray dry a fluid product having a viscosity ofhigher than 10 mPa·s using an outflow opening 6 of smaller than or equalto 150 μm, or a fluid product having a viscosity of higher than 25 mPa·susing an outflow opening of smaller than or equal to 150 μm, or a fluidproduct having a viscosity of higher than 50 mPa·s using an outflowopening of smaller than or equal to 150 μm, or a fluid product having aviscosity of higher than 100 mPa·s using an outflow opening of smallerthan or equal to 150 μm, or a fluid product having a viscosity of higherthan 200 mPa·s using an outflow opening of smaller than or equal to 150μm, or a fluid product having a viscosity of higher than 10 mPa·s usingan outflow opening of smaller than or equal to 100 μm, or a fluidproduct having a viscosity of higher than 25 mPa·s using an outflowopening of smaller than or equal to 100 μm, or a fluid product having aviscosity of higher than 50 mPa·s using an outflow opening of smallerthan or equal to 100 μm, or a fluid product having a viscosity of higherthan 100 mPa·s using an outflow opening of smaller than or equal to 100μm, or a fluid product having a viscosity of higher than 200 mPa·s usingan outflow opening of smaller than or equal to 100 μm, or a fluidproduct having a viscosity of higher than 10 mPa·s using an outflowopening of smaller than or equal to 80 μm, or a fluid product having aviscosity of higher than 25 mPa·s using an outflow opening of smallerthan or equal to 80 μm, or a fluid product having a viscosity of higherthan 50 mPa·s using an outflow opening of smaller than or equal to 80μm, or a fluid product having a viscosity of higher than 100 mPa·s usingan outflow opening of smaller than or equal to 80 μm, or a fluid producthaving a viscosity of higher than 200 mPa·s using an outflow opening ofsmaller than or equal to 80 μm, wherein the viscosity is defined at thespray drying temperature which in use prevails in the outflow opening,e.g. −50 to 300° C., in this example 40-100° C., and a shear rate as inuse present in the outflow opening, e.g. 1·10⁴-1·10⁶ s⁻¹, in thisexample 5·10⁵ s⁻¹, using a capillary viscosity meter.

Spray drying the high-viscosity fluid product with the above viscosity,is effected using the spraying device 2, having the above outflowopening 6, which is arranged to cause a pressure drop in the fluidproduct across the outflow opening 6 which is larger than 15 bar,preferably larger than 50 bar, more preferably larger than 100 bar, mostpreferably larger than 300 bar. The combination of the pressure drop,high viscosity and dimension of the outflow opening provide thatdroplets of the high-viscosity fluid product can be produced having adesired size, of e.g. smaller than or equal to 250 μm in average, whilethe amount of energy required to dry the droplets is reduced withrespect to conventional spray drying methods.

FIG. 2 shows an example of a second embodiment of an apparatus 1 forspray drying a fluid product according to the invention. In the exampleof FIG. 2 the spraying device 2 comprises feed pressure generating means12 for providing the fluid product to the outflow opening 6 at apredetermined feed pressure for obtaining a fluid jet. Here, the feedpressure generating means 12 are arranged for keeping the feed pressuresubstantially constant. Hence, a fluid jet is generated, while the feedpressure generating means 12 substantially do not disturb the jet.

In the example of FIG. 2, the feed pressure generating means comprise apump 14 for supplying the fluid product at the desired pressure. Thepump 14 may be arranged for keeping the feed pressure substantiallyconstant. Thereto, the pump may comprise a pressure regulator, such asfor instance an overpressure valve and/or a damper.

Alternatively, or additionally, the feed pressure generating means 12may be arranged for applying pressure to the fluid product hydraulicallyor pneumatically for keeping the feed pressure substantially constant,i.e. the feed pressure generating means 12 may use pressurized liquid orgas, respectively, to exert a substantially constant pressure on thefluid product.

Preferably, the feed pressure generating means 12 generate the feedpressure which is in the interval of 15-3000 bars, more preferably inthe interval of 15-600 bars. Hence, it is possible to spray dry thehigh-viscosity fluid product.

FIG. 3 shows an example of a third embodiment of an apparatus for spraydrying a fluid product according to the invention.

In the example of FIG. 3 the spraying device 12 comprises pressurevarying means 16 for varying the pressure of the fluid product upstreamof the outflow opening 6. When the jet is projected from the outflowopening, variations in the pressure of the fluid product of the jetcause the jet to contract at points of minimum pressure. Subsequently,the fluid jet will break up at the contractions, thus forming droplets.An amplitude of the variations in the pressure of the fluid product maybe approximately 10% of the feed pressure. The amplitude of thevariations in the pressure may be 1 mbar to 100 bar, preferably smallerthan or equal to 25 bar.

In this example, the pressure varying means 16 comprise a controlelement 18, which is movable in a direction from/to the outflow opening6. Vibrating the control element 18 relative to the outflow opening 6causes the pressure of the fluid product to vary between the controlelement 18 and the outflow opening 6. When the fluid product isprojected from the outflow opening 6 in the fluid jet, the variations inpressure in the fluid product extend into the jet.

The pressure varying means 16 may e.g. comprise a piezo-electricelement, an electrostrictive element, an acoustic element, anelectromagnetic actuator, a voice-coil, and/or mechanical means formoving the control element 18 in the direction from/to the outflowopening 6.

In a preferred embodiment, the control element 18 is positioned at apredetermined distance of 2-1500 μm, preferably 15-500 μm, to theoutflow opening 6. This provides the advantage that a pressure variationexerted to the high-viscosity fluid product is prevented from beingdamped by the high-viscosity fluid product to an extent that the jetprojected from the outflow opening does not experience a pressurevariation with large enough amplitude to effectively break up intodroplets.

In a particularly effective embodiment, the pressure varying means 16are arranged for varying the pressure of the fluid product upstream ofthe outflow opening 6 at a predetermined frequency. Preferably, thepredetermined frequency is substantially constant. Hence, the fluid jetwill contract, and subsequently break up, at substantially equidistantpositions along the fluid jet. Thus, substantially equal sized dropletswill be formed, providing droplets with a relatively narrow droplet sizedistribution, e.g. a droplet size distribution with a monodispersityindex of less than 1, preferably smaller than 0.7, more preferablysmaller than 0.1. The monodispersity index of the droplet sizedistribution is defined as (d₉₀−d₁₀)/d₅₀, wherein d₁₀, d₅₀ and d₉₀represent the 10%, 50% and 90% droplet size percentiles, respectively.

In this example, the predetermined frequency is chosen such that adistance between two droplets consecutively ejected at the outflowopening 6 is greater than or equal to two times the droplet diameter,preferably greater than or equal to three times the droplet diameter.Thus, coagulation of droplets can be prevented, maintaining a narrowdroplet size distribution.

In this example the predetermined frequency is in the interval of500-200000 Hz. For example, when using a fluid product having aviscosity of 50 mPa·s and using an outflow opening having a transversedimension, e.g. a smallest transverse dimension such as a diameter, of80 μm, the frequency may be chosen between 500 and 40000 Hz forobtaining droplets with an average size (d₅₀) of 133 μm to 575 μmdepending on chosen frequency and volume flow of fluid product throughthe outflow opening.

In the examples of FIGS. 1-3 the spraying device 2 comprises one outflowopening 6. It will be appreciated that it is also possible that thespraying device 2 comprises a plurality of outflow openings 6 forprojecting the fluid product out of the plurality of outflow openingsfor obtaining droplets of the fluid product. Thereto, the outflowopenings may e.g. may be arranged as bores in a surface of the sprayingdevice. The plurality of outflow openings may be arranged for generatinga plurality of mutually divergent jets of the fluid product. Thereto,the outflow openings may e.g. may be arranged as bores in a surface ofthe spraying device, which bores extend in mutually divergingdirections, e.g. in directions which are non-perpendicular with respectto the surface of the spraying device 2. When the jets are mutuallydivergent, the risk of coagulation of droplets ejected by mutuallydifferent outflow openings is reduced, since a distance between thedroplets ejected by the mutually different outflow openings increasesduring flight. It is possible to use the plurality of outflow openingsin combination with a single control element for varying the pressure ofsubstantially all fluid jets generated by the plurality of outflowopenings.

Preferably, the outflow openings of the plurality of outflow openingshave substantially identical dimensions, to allow droplets ofsubstantially identical dimensions to be ejected from each separateoutflow opening, hence allowing the droplets to be produced with therelatively narrow size distribution.

Preferably, a distance between two adjacent outflow openings of theplurality of outflow openings is larger than 1.5 times a transversedimension, such as a diameter, of at least one of the two adjacentoutflow openings, more preferably larger than 2 times, most preferablylarger than or equal to 2.5 times the transverse dimension. Hence, therisk of coagulation of droplets ejected by mutually different outflowopenings is reduced. Preferably, a distance between two adjacent outflowopenings of the plurality of outflow openings is smaller than 5 times atransverse dimension, such as a diameter, of at least one of the twoadjacent outflow openings, more preferably smaller than 4 times, mostpreferably smaller than or equal to 3 times the transverse dimension.Hence, a physical size of the spraying device 2 may be limited.

FIGS. 4 a-4 g show examples of plan views of the plurality of outflowopenings 6 of embodiments of the spraying device 2 according to theinvention. In the examples of FIGS. 4 a-4 d, the plurality of outflowopenings 6 is arranged in a substantially ring-shaped formation 20. InFIG. 4 a an example is shown of a ring of closely packed outflowopenings, e.g. in hexagonal close packing. Hence, a hollow cone ofdroplets may be generated. In FIG. 4 b an example is shown of a ringcomprising a single endless line of outflow openings. The single line ofoutflow openings reduces the risk of coagulation of droplets. In FIG. 4c an example is shown wherein the plurality of outflow openings isarranged in a formation comprising a plurality of substantiallyring-shaped sub-formations, here three spaced concentric rings eachcomprising a single endless line of outflow openings. The spaced singleline rings reduce the risk of coagulation of droplets, while reducingthe surface area size required for providing a predetermined number ofoutflow openings, with respect to the example of FIG. 4 b. In FIG. 4 dan example is shown wherein the plurality of outflow openings isarranged in a formation comprising a plurality of substantiallyring-shaped sub-formations, here five non-concentric rings eachcomprising a single endless line of outflow openings.

FIG. 4 e shows an example of a circle of closely packed outflowopenings, e.g. in hexagonal close packing. Hence, a full cone ofdroplets may be produced, giving a large number of droplets per unitsurface area of spraying device comprising outflow openings. Hence, acompact spray drying apparatus may be provided.

FIG. 4 f shows an example of a substantially straight line of outflowopenings. This e.g. allows for spray drying into a narrow wide vessel.FIG. 4 g shows an example of a plurality of spaced substantiallystraight lines of outflow openings.

According to the invention a method for spray drying a high-viscosityfluid product is provided. This method can e.g. be performed using thespraying device 2 according to any one of the Figures. The methodcomprises projecting the fluid product out of the outflow opening 6 ofthe spraying device 2 for obtaining droplets of the fluid product,wherein the spraying device 2 is arranged to cause a pressure drop inthe fluid product across the outflow opening 6 which is larger than 15bar, and at least partially drying the droplets in a drying medium, suchas air, to become particles.

As already explained with respect to the apparatus 1, the pressure dropis preferably larger than 50 bar, more preferably larger than 100 bar,most preferably larger than 300 bar.

Using the method according to the invention, a powder may be produced.The powder may have a monodispersity index smaller than 1, preferablysmaller than 0.7, more preferably smaller than 0.1. The monodispersityindex of the powder is defined as (d₉₀−d₁₀)/d₅₀, wherein d₁₀, d₅₀ andd₉₀ represent the 10%, 50% and 90% particle size percentiles of thepowder, respectively. The powder may have an average particle diametersmaller than or equal to 250 μm.

According to the invention, the powder is produced from thehigh-viscosity fluid product by spray drying. As already mentioned thishas the advantage, that the fluid product to be spray dried may compriserelatively large concentrations of dry matter, so that relatively smallamounts of solvent have to be removed from droplets expelled by theoutflow opening to yield dry particles. Without wishing to be bound byany theory, it is believed that this causes less inclusion of solventwithin a dry outer crust of the particle, so that after drying particlesare obtained with lower porosity and/or a lower percentage of includedgas. Hence, using the method according to the invention, it is possibleto produce the powder having small percentage of the volume of theparticles consisting of gas and/or voids, e.g. less than 5% of a volumeof particles of the powder consists of gas and/or voids. Further, usingthe method according to the invention, it is possible to produce thepowder having a high density, e.g. having a bulk density larger than orequal to 550 kg/m³ or preferably larger than or equal to 650 kg/m³ forfood powders, generally mainly comprising fat, protein and/orcarbohydrates.

For food powders comprising fat a bulk density may be obtained which ishigher than a reference bulk density according to the equation

RBD=ZFD−5×FC

wherein RBD represents the reference bulk density in kg/m³, ZFDrepresents a zero-fat-density which represents the bulk density (inkg/m³) of a powder containing no fat, and FC represents the fat contentin percents by weight of the dried product. Using the spray dryingmethod according to the invention, a powder may be obtained having bulkdensity (in kg/m³) which is higher than the RBD according to the aboveequation wherein ZFD is equal to or larger than 650 kg/m³, preferablyequal to or larger than 800 kg/m³.

Exemplary powders were produced using the spray drying method accordingto the invention. A first powder had a fat content of 50% by weight anda bulk density of 540 kg/m³. A second powder had a fat content of 78percent by weight and a bulk density of 420 kg/m³.

EXAMPLE 1

The production of highly monodisperse maltodextrin powder was conductedaccording to the following procedure:

A solution of 60% by weight maltodextrin and 40% by weight of water wasprepared, having a density of 1250 mg/ml. This solution was fed into ahigh viscosity spraying device as described hereinabove. The sprayingdevice used has a substantially circular outflow opening with a diameterof 50 micrometers. The solution was projected out of the outflow openingwith a feed rate of 1.25 ml/min, and a firing frequency of 23.7 kHz(i.e. droplets were produced at a rate of 23.7·10³ droplets per second).The temperature of the spraying device at the outflow opening was 80° C.and the feed pressure applied in the spraying device was 35 bar. Theresulting droplets had an average diameter of 120 μm.

To dry these droplets to obtain a monodisperse powder, the droplets wereejected into a spray drying tower with an entrance temperature of 170°C. and exit temperature of 85° C. The running length for drying was 1.8meter and the venting percentage was 60%, which resulted in an averageresidence time of 2-6 s for each droplet. The particles of the resultingpowder produced had an average diameter of 95 μm and a monodispersityindex of 0.60. The powder produced had a bulk density of 840 kg/m³.

EXAMPLE 2

Monodisperse creamer-powder was produced according to the followingprocedure.

A solution of 30% by weight water, 3% by weight Sodium Caseinate, and38% by weight maltodextrin was prepared, into which 29% by weightsunflower oil was emulsified using a high pressure homogeniser. Theemulsion had a viscosity of 30-40 mPa·s at 85° C. and high shear (5·10⁵s⁻¹) and a viscosity of 700-900 mPa·s at low shear (300 s⁻¹) and 20° C.,both measured with a capillary viscosity meter.

This solution was fed into a high viscosity spraying device as describedhereinabove, having a substantially circular outflow opening with adiameter of 50 micrometers. The solution was projected out of theoutflow opening with a feed rate of 1 ml/min, and a firing frequency of25 kHz. The temperature of the spraying device at the outflow openingwas 73° C. and the feed pressure applied in the spraying device was 60bar. To dry the droplets produced to obtain monodisperse powder, thedroplets were ejected into a spray drying tower with an entrancetemperature of 129° C. and exit temperature of 85° C. The running lengthfor drying was 1.8 meter and the venting percentage was 60%, whichresulted in an average residence time of 2-6 s for each droplet. Theresulting powder produced had an average particle diameter of 147 μm anda monodispersity index of 0.69. The powder produced had a bulk densityof 550 kg/m³.

The method and apparatus according to the invention may be used forspray drying products such as a nutrient or an ingredient therefore,e.g. dairy products, proteins, carbon hydrates, fats, or combinationsthereof. Alternative products are, however, not excluded.

In the foregoing specification, the invention has been described withreference to specific examples of embodiments of the invention. It will,however, be evident that various modifications and changes may be madetherein without departing from the broader spirit and scope of theinvention as set forth in the appended claims. For example, instead offor spray drying nutrients or ingredients therefore, the method may alsobe used for spray drying other products such as, but not limited to,detergents, pigments, catalysts, pharmaceuticals, cosmetics, polymericresins, ceramic powders, powder coating materials, adhesives, gypsum,cement, metal powders, etc.

However, other modifications, variations and alternatives are alsopossible. The specifications, drawings and examples are, accordingly, tobe regarded in an illustrative rather than in a restrictive sense.

In the claims, any reference signs placed between parentheses shall notbe construed as limiting the claim. The word ‘comprising’ does notexclude the presence of other features or steps then those listed in aclaim. Furthermore, the words ‘a’ and ‘an’ shall not be construed aslimited to ‘only one’, but instead are used to mean ‘at least one’, anddo not exclude a plurality. The mere fact that certain measures arerecited in mutually different claims does not indicate that acombination of these measures cannot be used to advantage.

1. A method for spray drying a high-viscosity fluid product using aspraying device, comprising the steps of: projecting the fluid productout of an outflow opening of the spraying device for obtaining dropletsof the fluid product, wherein the spraying device is arranged to cause apressure drop in the fluid product across the outflow opening which islarger than 15 bar; and at least partially drying the droplets in adrying medium, such as air, to become particles.
 2. The method accordingto claim 1, wherein the pressure drop is larger than 50 bar, preferablylarger than 100 bar, most preferably larger than 300 bar.
 3. The methodaccording to claim 1, wherein the pressure drop is in the interval of15-3000 bar, preferably in the interval of 50-600 bar.
 4. The methodaccording to claim 1, wherein the step of projecting the fluid productout of the outflow opening comprises: generating a fluid jet projectingfrom the outflow opening; and disturbing the fluid jet for breaking thefluid jet into droplets with a narrow size distribution.
 5. The methodaccording to claim 1, wherein the step of projecting the fluid productout of the outflow opening comprises: providing the fluid product to anoutflow opening at a predetermined feed pressure.
 6. The methodaccording to claim 4, wherein the step of disturbing the fluid jetcomprises: varying the pressure of the fluid product upstream of theoutflow opening.
 7. The method according to claim 6, wherein the step ofvarying the pressure comprises: moving an end of a control element in adirection from/to the outflow opening at a predetermined distance to theoutflow opening for varying the pressure of the fluid product byvibrating the control element.
 8. The method according to claim 7,wherein the predetermined distance is 2-1500 μm, preferably 15-500 μm.9. The method according to claim 7, wherein the control element isvibrated using at least one of a piezo-electric element, anelectrostrictive element, an acoustic element, an electromagneticactuator, a voice-coil, or mechanical means.
 10. The method according toclaim 6, wherein the pressure of the fluid product upstream of theoutflow opening is varied at a predetermined, substantially constant,frequency.
 11. The method according to claim 10, wherein a dropletdiameter is determined by controlling the predetermined frequency and/ormaterial throughput through the outflow opening.
 12. The methodaccording to claim 10, wherein the predetermined frequency is chosensuch that a distance between two droplets consecutively ejected at theoutflow opening is greater than or equal to two times the dropletdiameter, preferably greater than or equal to three times the dropletdiameter.
 13. The method according to claim 9, wherein the predeterminedfrequency is in the interval of 500-200000 Hz.
 14. The method accordingto claim 1 further comprising the steps of projecting the fluid productout of a plurality of outflow openings of the spraying device forobtaining droplets of the fluid product.
 15. The method according toclaim 1, wherein a viscosity of the fluid product, determined at a spraydrying temperature which in use prevails in the outflow opening, such as−50 to 300° C., e.g. 40-100° C., and a shear rate as in use present inthe outflow opening, e.g. 1·104-1·106 s−1, using a capillary viscositymeter, is higher than 10 mPa·s, preferably higher than 25 mPa·s, morepreferably higher than 50 mPa·s, even more preferably higher than 100mPa·s, most preferably higher than 200 mPa·s.
 16. The method accordingto claim 1, wherein a transverse dimension, e.g. a smallest transversedimension such as a diameter, of the outflow opening is smaller than orequal to 150 μm, preferably smaller than or equal to 100 μm, morepreferably smaller than or equal to 80 μm.
 17. The method according toclaim 5, wherein the feed pressure is kept substantially constant. 18.The method according to claim 17, wherein the feed pressure is keptsubstantially constant by means of applying a pressure to the fluidproduct hydraulically or pneumatically.
 19. The method according toclaim 17, wherein the feed pressure is kept substantially constant bymeans of a pump.
 20. The method according to claim 1, wherein the feedpressure is in the interval of 15-3000 bars, preferably in the intervalof 15-600 bars.
 21. A powder produced using the method according toclaim
 1. 22. The powder according to claim 21 having a monodispersityindex smaller than 1, preferably smaller than 0.7, more preferablysmaller than 0.1.
 23. The powder according to claim 21, having anaverage particle diameter (d50) smaller than or equal to 250 μm.
 24. Thepowder according to claim 21, wherein less than 5% of the volume of thepowder particles consists of gas and/or voids.
 25. The powder accordingto claim 21, comprising a food product mainly comprising protein,carbohydrate, fat, or a combination thereof.
 26. The powder according toclaim 21 having a bulk density larger than or equal to 550 kg/m3,preferably larger than or equal to 650 kg/m3.
 27. The powder accordingto claim 21, comprising fat, having a bulk density higher than areference bulk density according to the equationRBD=ZFD−5×FC wherein RBD represents the reference bulk density in kg/m3,ZFD represents a zero-fat-density which represents the bulk density (inkg/m3) of a powder containing no fat, and FC represents the fat contentof the powder in percents by weight, wherein ZFD is equal to or largerthan 650 kg/m3, preferably equal to or larger than 800 kg/m3.
 28. Anapparatus for spray drying a high-viscosity fluid product comprising aspraying device arranged for projecting the fluid product out of anoutflow opening of the spraying device for obtaining droplets of thefluid product, wherein the spraying device is arranged to cause apressure drop in the fluid product across the outflow opening which islarger than 15 bar; and drying means for causing and/or allowing thedroplets to dry to become particles.
 29. The apparatus according toclaim 28 wherein the pressure drop is larger than 50 bar, preferablylarger than 100 bar, most preferably larger than 300 bar.
 30. Theapparatus according to claim 28, wherein the spraying device comprisesfeed pressure generating means for providing the fluid product to theoutflow opening at a predetermined feed pressure for obtaining a fluidjet.
 31. The apparatus according to claim 28, wherein the sprayingdevice comprises pressure varying means for varying the pressure of thefluid product upstream of the outflow opening for breaking the fluid jetinto droplets with a narrow size distribution;
 32. The apparatusaccording to claim 31, wherein the pressure varying means comprise acontrol element which is movable in a direction from/to the outflowopening at a predetermined distance of 2-1500 μm, preferably 15-500 μm,to the outflow opening for varying the pressure of the fluid product byvibrating the control element.
 33. The apparatus according to claim 32,wherein the pressure varying means are arranged for vibrating thecontrol element using at least one of a piezo-electric element, anelectrostrictive element, an acoustic element, an electromagneticactuator, a voice-coil, or mechanical means.
 34. The apparatus accordingto claim 31, wherein the pressure varying means are arranged for varyingthe pressure of the fluid product upstream of the outflow opening at apredetermined substantially constant frequency.
 35. The apparatusaccording to claim 34, wherein the predetermined frequency is chosensuch that a distance between two droplets consecutively ejected at theoutflow opening is greater than or equal to two times the dropletdiameter, preferably greater than or equal to three times the dropletdiameter.
 36. The apparatus according to claim 34, wherein thepredetermined frequency is in the interval of 500-200000 Hz.
 37. Theapparatus according to claim 30, wherein the feed pressure generatingmeans are arranged for keeping the feed pressure substantially constant.38. The apparatus according to claim 37, wherein the feed pressuregenerating means are arranged for applying pressure to the fluid producthydraulically or pneumatically for keeping the feed pressuresubstantially constant.
 39. The apparatus according to claim 37, whereinthe feed pressure generating means comprise a pump for keeping the feedpressure substantially constant.
 40. The apparatus according to claim28, wherein the feed pressure generating means are arranged forgenerating the feed pressure which is in the interval of 15-3000 bars,preferably in the interval of 15-600 bars.
 41. The apparatus accordingto claim 28, wherein a transverse dimension, e.g. a smallest transversedimension such as a diameter, of the outflow opening is smaller than orequal to 150 μm, preferably smaller than or equal to 100 μm, morepreferably smaller than or equal to 80 μm.
 42. The apparatus accordingto claim 28, wherein the spraying device comprises a plurality ofoutflow openings for projecting the fluid product out of the pluralityof outflow openings for obtaining droplets of the fluid product.
 43. Theapparatus according to claim 42, wherein the plurality of outflowopenings is arranged for generating a plurality of mutually divergentjets of the fluid product.
 44. The apparatus according to claim 42,wherein a distance between two adjacent outflow openings of theplurality of outflow openings is larger than 1.5 times a transversedimension, e.g. a smallest transverse dimension such as a diameter, ofat least one of the two adjacent outflow openings, preferably largerthan 2 times the transverse dimension, more preferably larger than 2.5times the transverse dimension.
 45. The apparatus according to claim 42,wherein a distance between two adjacent outflow openings of theplurality of outflow openings is smaller than 5 times a transversedimension, e.g. a smallest transverse dimension such as a diameter, ofat least one of the two adjacent outflow openings, preferably smallerthan 4 times the transverse dimension, more preferably smaller than 3times the transverse dimension.
 46. The apparatus according to claim 42,wherein the plurality of outflow openings is arranged in a substantiallyring-shaped formation.
 47. The apparatus according to claim 42, whereinthe plurality of outflow openings is arranged in a formation comprisinga plurality of substantially ring-shaped sub-formations.
 48. Theapparatus according to claim 42, wherein the plurality of outflowopenings is arranged in a substantially straight line.
 49. A sprayingdevice of the apparatus according to claim 28.